超深层灰岩盖层的脆—韧性——以四川盆地元坝气藏为例

中国含油气盆地超深层广泛发育灰岩，灰岩的主要矿物成分是方解石，其特殊的晶体结构决定了其在超深层具有很强的塑性和韧性。在小变形作用下，灰岩不容易发生断裂。灰岩尤其是泥灰岩，因其较低的孔隙度和渗透率也可以作为盖层。四川盆地元坝气藏埋深超过6 500 m，储气规模大，其盖层和保存条件一直备受关注。下三叠统膏盐岩作为元坝气藏的区域性盖层得到普遍认可，但是飞仙关组灰岩作为其直接盖层尚存争议。在岩心观察、岩石力学参数测试、地质资料分析的基础上，从脆—韧性的角度分析飞仙关组灰岩作为盖层的完整性。飞仙关组灰岩在生气高峰期及之后，韧性显著提高，力学性质处于韧性阶段，不易发生破裂，能够保持岩层完整性，从而成为二叠系长兴组白云岩储层的良好盖层。该实例说明，灰岩在超深层可以作为盖层，对碳酸盐岩区的油气勘探具有重要意义。

Brittle-ductile property of ultra-deep limestone cap: Case study of Yuanba gas reservoir in Sichuan Basin

Limestone is widely developed in ultra-deep layers of petroliferous basins in China. The main mineral component of limestone is calcite. Its special crystal structure determines that it has strong plasticity and toughness in ultra-deep layers. It is not prone to fracture under small deformations. Limestone, especially marl, can also act as caprock due to its low porosity and permeability. The Yuanba gas reservoir of Sichuan Basin has a burial depth of more than 6 500 m and a large scale of gas storage. Its caprock and preservation conditions have always attracted attention. The Lower Triassic gypsum-salt rock is generally accepted as the regional caprock of the Yuanba gas reservoir, but the Feixianguan Formation limestone is still controversial as its direct caprock. Based on core observations, rock mechanical parameter testing, and geological data analysis, the integrity of Feixianguan Formation limestone as caprock is analyzed from the point of brittle-ductile property. During and after the peak gas generation period, the limestone of Feixianguan Formation has significantly improved ductile property, and its mechanical properties are in the ductile stage. It is not easy to fracture, and can maintain the integrity of the rock formation. It becomes a good caprock for dolomite reservoir of the Permian Changxing Formation. This example shows that limestone can act as a caprock in ultra-deep layers, which is of great significance for oil and gas exploration in the ultra-deep carbonate rock area.